Cryptococcus neoformans, the major etiological agent of Cryptococcosis, is a primary cause of opportunistic infections in AIDS patients. Four serotypes (A-D) of C. neoformans are distinguished; they differ in the structure of the glucuronoxylomannans (GXMs), capsular polysaccharides on their outer surface. Primary structural characterization of these GXMs is the first step in understanding the epitope specificity corresponding to the individual serotypes. We have previously determined the structures of the repeat hepta- and pentasaccharide units, at the level of the de-O-acylated intact polysaccharides of C. neoformans serogroups B and D, respectively, by a combination of two-dimensional {1H,1H} TOCSY, COSY, ROESY, and {1H,13C} HMQC NMR spectroscopy. The conformation and dynamics of the GXM from serotype D was studied by NMR spectroscopy and molecular modeling. The sample was enriched with 13C by growing the yeast on [U-13C]-glucose-containing medium. This allowed the measurement of inter-glycosidic 1H-13C coupling constants that were combined with {1H} NOE values from NOESY buildup curves in order to determine glycosidic torsion angles. The experimental values were compared to energy minimized structures calculated with the PIM carbohydrate parameterization of the TRIPOS force field. 13C Relaxation rates (T1, T2, and heteronuclear NOE) could also be readily measured on the enriched sample and were used to generate relative correlation times for residues. In this analysis, simplifying assumptions (e.g., isotropic tumbling) were applied; future work on related systems will consider more sophisticated models for fitting the data. However, the data are compatible with greater mobility of the side chain relative to backbone residues. The goal of further analysis of other, more highly branched serotypes is to determine the relationships between the degree of biological activity and 3D structure and dynamics.